The Iraqi government's Shiite bloc reached an agreement earlier in the day with a group of mostly Sunni lawmakers to secure the measure's passage.
In exchange for their vote, the Sunnis won a major concession from the pact's staunch supporters; a national referendum will be held on the agreement.
Salim Abdullah, the spokesman for the largest Sunni bloc in parliament, earlier confirmed that a deal was reached and that his 44-seat bloc, the Iraqi Accordance Front, would support the security pact in Thursday's vote.
He said the agreement met the demand by his bloc and smaller groups that a referendum on the pact be held by July 30. That means the deal could be approved by Parliament, but torpedoed by a "no" vote in the referendum.
Shiite lawmakers Khalid al-Attiyah, Sami al-Askari and Ali al-Adeeb told the Associate Press that the deal did not include two other key Sunni demands: the repeal of a law designed to weed out former members of Saddam Hussein's Baath party, and the dissolution of a special court that tried the dictator and top officials of his regime. Saddam was sentenced to death and executed in 2006.
The security pact meets an Iraqi goal of a clear timetable for the departure of American forces and has been described by Prime Minister Nouri al-Maliki as a path toward full sovereignty for Iraq.
White House press secretary Dana Perino called the vote "an incredible success story for our military and for the Iraqi Security Forces."
"The June 2009 date is consistent with the Joint Campaign Plan, and the end of 2011 date should give U.S. forces and the ISF enough time to solidify gains made in the last year," Perino added.
But CBS News correspondent Elizabeth Palmer reported from Baghdad that, while most military analysts say the Iraqis are not ready to take over security duties yet, there is broad recognition that the national forces have made huge strides in the last year.
One small but symbolic piece of evidence of that improvement came Thursday as U.S. troops at Falcon Base, south of Baghdad, enjoyed a Thanksgiving feast - alongside their Iraqi counterparts.
Palmer reports that mistrust between American and Iraqi troops is genuinely starting to melt away as they work more closely together.
With the Status of Forces agreement specifying that, essentially, U.S. troops will be confined to their bases in Iraq as of June 2009, those Iraqi counterparts are now mere months away from taking the lead.
The parliamentary debate over the proposal was subsumed by sectarian-based disputes among political factions that have stalled efforts to achieve national reconciliation nearly six years after Saddam's ouster. The haggling among political factions delayed the vote, which was originally scheduled for Wednesday.
Iraq's Shiites and Kurds, who comprise about 80 percent of Iraq's 27 million people, were the target of massacres and other atrocities under Saddam's Sunni-dominated regime. Grievances run deep, and caving in to Sunni demands on the special court and the Baathist law could have produced voter backlash ahead of provincial and general elections in 2009.
Lawmakers were under additional pressure to vote on the security pact because the legislature is expected to go into recess in the next few days because of an Islamic holiday.
Now that parliament has approved the pact, it must be ratified by the Presidential Council, whose three members each have veto power.
The U.N. mandate governing the presence of U.S. troops in Iraq expires Dec. 31, and the pact will provide legal cover for the troops to remain.
Under the deal, U.S. forces will withdraw from Iraqi cities by June 30 and the entire country by Jan. 1, 2012. Iraq will also have strict oversight over U.S. forces. The U.N. mandate that currently governs American troops gives them freer rein, leading to Iraqi complaints that they are an occupying force intent on preserving U.S. interests in the Middle East.
Earlier, al-Maliki's ruling coalition appeared to be assured of a slim majority in the legislature of about 140 seats. But he sought a bigger win that transcends religious and sectarian divisions and reinforces the legitimacy of the pact. He achieved that wide margin with the Sunni bloc's votes.
The wide margin met the demands of the country's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, who had indicated that the deal would be acceptable only if passed by a comfortable majority. The cleric is revered by Iraq's majority Shiites, and he could have sunk the deal if he had publicly spoken against it.